It irks me if people don't say thank you.
If I am putting my kids on and someone is allready on or about to climb on I will offer do they want a ride.
If my boys go to run towards one when someone else is putting money in I hold them back as don't want them free loading, if someone offers and says let them on I will and say thank you, and often will then pay for another ride with there child as well.

It is rude to not say thank you and its rude to rush kids on when see someone else putting money in.